One of the leading challenges facing designers of wireless products is achieving acceptable battery life without requiring large batteries that would impact the weight and form factor of the product. An important step in increasing battery life of wireless devices is to reduce the power consumed by integrated circuits (ICs) inside the device.
Integrated circuits are typically specified with a guaranteed operating voltage range. The manufacturer guarantees operation above a minimum voltage termed Vcc(min), and below a maximum operating voltage termed Vcc(max). A somewhat higher “Absolute Maximum” supply voltage is also specified above which damage to the IC may occur. Operation from a supply greater than Vcc(max) but lower than the absolute maximum is not guaranteed, but no damage will result to the IC.
In practice, most ICs will operate correctly somewhat below Vcc(min). In order to guarantee operation at a specified Vcc(min), IC manufacturers typically test operation both slightly above the maximum rated temperature, and slightly below the minimum rated temperature at a voltage somewhat below Vcc(min). The voltage at which an IC will cease to operate correctly will generally therefore be below the Vcc(min), and in many cases well below Vcc(min) if the device is operated at room temperature.
In one example, an IC may be rated with a Vcc(min) of 2.7V and Vcc(max) of 3.6V, with an operating temperature range of 0 to 70 degrees Celsius. The IC manufacturer may test every device at 2.6V at both minus 10 and plus 80 degrees Celsius. In this example, a typical instance of the IC may work correctly in all respects down to 2.5V, and with degraded performance down to 2.3V, provided that the temperature of operation is constrained to a smaller range than that specified, for example plus 10 to minus 40 degrees. In some cases, it may be easy to determine whether or not an IC being supplied with a lower voltage than specified is performing correctly; in other cases, it may not.
Many ICs are used in battery powered applications where the output voltage range of the batteries does not match the operating voltage range of the IC. In such cases, there may be a number of different ICs, with different operating voltage ranges. In this case, it is common to use a direct current to direct current (DC-DC) boost converter to supply an approximately constant voltage to all ICs, ensuring correct operation of the ICs regardless of the output voltage of the batteries. A disadvantage of this approach is that for part of the life of the batteries the output may be being boosted unnecessarily, causing the batteries to be drained more quickly than necessary.